1. Field of the Invention
This invention relates to an apparatus and method for cleaning semiconductor substrates or other such items requiring extremely high levels of cleanliness.
2. Description of the Related Art
Semiconductor substrates can be cleaned by propagating acoustic energy, such as megasonic energy, into a layer of cleaning solution on the surface of the substrate. Megasonic cleaning systems use this cleaning solution layer to propagate megasonic energy, i.e. acoustic energy at frequencies much greater than ultrasonic. This energy is directed toward the surface of the substrate and thereby removes, safely and effectively, particles from the substrate surface without the negative side effects associated with ultrasonic cleaning.
In the past, such cleaning systems have been designed to process substrates in batches, typically cleaning 25 substrate at once. The benefit of this batch cleaning became less important as substrate size increased because single substrate capacity increased. Also, substrate processors began working with more delicate devices, which required more careful handling than was possible in batch cleaning. The greater value per substrate and the more delicate nature of the devices produced on the substrates created a great need for single wafer processing equipment.
Single substrate megasonic cleaning equipment for processing the larger substrates carrying more delicate devices have been developed to meet this need. One such single substrate cleaning system incorporates a probe and a transducer and is described in U.S. Pat. No. 6,140,744 and commercially available from Verteq Inc. of Santa Ana, Calif. One cleaning apparatus described therein comprises an elongate probe configured to propagate megasonic energy to a surface of a substrate by way of a meniscus of liquid extending between the probe and the substrate. Because the energy is transmitted through a meniscus of liquid, the process is a xe2x80x9cwetxe2x80x9d process and it requires the probe to be positioned very close to the substrate surface.
After this xe2x80x9cwetxe2x80x9d cleaning process, the substrate must be dried prior to further processing. Various methods of drying the substrate have been tried and have generally involved spinning the substrate and thereby forcing the liquid off the substrate surface via centrifugal forces arising from the spinning. Unfortunately, this drying method has its drawbacks, such as the tendency of liquid on a surface to leave behind residue, e.g. water spots. In the past, such spots were not of great concern to the simpler devices being produced on the substrates. However, as already mentioned, the devices processed on substrates have become more delicate, and therefore more sensitive to contaminants of all kinds, including water spots. Moreover, substrate processors have become more aware of sources of process variation, which translate into variation in performance of the devices and yield variation. One such source of these variations is contaminants, including drying residue. Therefore, careful control of the drying conditions has been investigated by some.
European patent application publication EP0905747A1 to IMEC discloses a drying apparatus that exploits rotational and Marangoni effects to improve drying performance. As mentioned above, the rotation of the substrate subjects the liquid to centrifugal forces, which tend to force the liquid from the center of the substrate toward its edge, and ultimately off of the surface. Simultaneously, a surface tension reducing vapor creates the so called Marangoni effect that reduces the tendency of the liquid to adhere to the substrate surface, i.e. reduces the liquid surface tension. This reduces the tendency of the liquid to remain on the substrate surface long enough to evaporate from the surface and therefore helps to produce a residue free drying process. While the IMEC apparatus has achieved satisfactory substrate drying results in the laboratory, the concept has not been implemented into a commercial application.
Another issue presented by wet spin cleaning and drying of substrates is the containment and disposal of the process liquids involved, for example, various acids, bases, solvents, and de-ionized water. Some of these liquids may harm workers or damage other equipment in the vicinity of the cleaning apparatus if the workers or equipment come into contact with the process liquids. Thus, full containment and removal of the process liquids is necessary to maintain a safe working environment and protect valuable equipment.
However, a critical design consideration for any machine in substrate processing is process time, or through-put. This is in part because substrate processing must be done in very clean, and thus very expensive, fabrication facilities. As a result, substrate processors prefer to maximize the output of existing facilities rather than expanding those facilities or building new ones. Thus, fast through-put is preferred.
Therefore, a need exists for an improved cleaning method and apparatus that will improve the drying performance in a single wafer processing application and will improve throughput for performing substrate cleaning and drying operations.
In one embodiment, the present invention is a method of cleaning and drying a generally flat substrate positioned on a rotatable support is provided. A transmitter is positioned closely spaced above an upper surface of the substrate. Fluid is applied to the substrate to create a meniscus between the transmitter and the rotating substrate. Megasonic energy is applied to the transmitter to cause it to propagate megasonic energy through the meniscus to the substrate to loosen particles on the substrate while the substrate is rotating at a first rate. The transmitter is retracted. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to the upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly support arm is moved into place as the transmitter is being retracted.
In another embodiment, a method of cleaning and drying a generally flat substrate positioned on a rotatable support is provided. A surface of the substrate is cleaned. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to the upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly support arm is retracted radially outwardly at a retraction rate to a periphery of the substrate while liquid is applied to the substrate through the liquid outlet. Then, the drying vapor is applied to the substrate to dry the substrate. The substrate drying assembly support arm is retracted at a substrate-center retraction rate near the center of the substrate and a substrate-periphery retraction rate near the periphery of the substrate. The substrate-center retraction rate is faster than the substrate-periphery retraction rate.
In another embodiment, a method of cleaning and drying a generally flat substrate positioned on a rotatable support is provided. A surface of the substrate is cleaned. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to the upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly support arm is retracted radially outwardly at a retraction rate to a periphery of the substrate while liquid is applied to the substrate through the liquid outlet. Then, the drying vapor is applied to the substrate to dry the substrate. At a location between the center of the substrate and the periphery of the substrate, the retraction rate of the substrate drying assembly support arm is greater than the retraction rate near the center of the substrate and greater than the retraction rate near the periphery of the substrate.
In another embodiment, a method of cleaning and drying a generally flat substrate positioned on a rotatable support is provided. A surface of the substrate is cleaned. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to the upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly support arm is retracted radially outwardly at a retraction rate to a periphery of the substrate while liquid is applied to the substrate through the liquid outlet. Then, the drying vapor is applied to the substrate to dry the substrate. The substrate is rotated in a range between about 50 rpm and about 1,000 rpm while the retraction rate is in the range between about 1 mm per second and about 20 mm per second.
In another embodiment, a method of drying a generally flat substrate that has been cleaned is provided, where the substrate has been positioned on a rotatable support. At least one of a blanket substrate drying process window if the substrate has a blanket portion or a patterned substrate drying process window if the substrate has a patterned portion is selected. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate is rotated. The substrate drying assembly support arm is retracted radially outwardly according to the selected drying process window to a periphery of the substrate while liquid is applied to the substrate through the liquid applying outlet. Then, the drying vapor being applied to the substrate to dry the substrate.
In another embodiment, a method of drying a generally flat substrate that has been cleaned is provided, where the substrate is positioned on a rotatable support. A substrate drying assembly support arm of a substrate drying assembly is moved into position closely spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and includes an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly support arm is retracted radially outwardly at a retraction rate to a periphery of the substrate while liquid is being applied to the substrate through the liquid applying outlet. Then, the drying vapor is applied to the substrate to dry the substrate. The substrate drying assembly support arm is retracted at a substrate-center retraction rate near the center of the substrate and a substrate-periphery retraction rate near the periphery of the substrate. The substrate-center retraction rate is faster than the substrate-periphery retraction rate.
In another embodiment, an apparatus for cleaning and drying a generally flat substrate includes a substrate support positioned within a process bowl, a transmitter, a fluid dispenser, a substrate drying assembly, and a controller. The transmitter is configured to be spaced above the substrate, to propagate megasonic energy, and to be extendable into and out of the process bowl. The fluid dispenser applies fluid to a surface of the substrate. The substrate drying assembly is configured to be spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is extendable into and out of the process bowl. The controller causes the transmitter and the substrate drying assembly to be extended from the edge of the process bowl to a position over the surface of the substrate, and causes the transmitter to be retracted from the process bowl as the substrate drying assembly is being extended.
In another embodiment, an apparatus for cleaning and drying a generally flat substrate comprises a rotatable support for supporting the substrate, a transmitter, a fluid dispenser, a substrate drying assembly, and a controller. The rotatable support is positioned within a process bowl. The transmitter is configured to be spaced above the substrate, to propagate megasonic energy, and to be extendable into and out of the process bowl. The fluid dispenser applies fluid to a surface of the substrate. The substrate drying assembly is configured to be spaced above the substrate. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is configured to be extendable into and out of the process bowl. The controller causes the transmitter and the substrate drying assembly to be extended from the edge of the process bowl to a position over the surface of the substrate. The controller also causes the transmitter and the substrate drying assembly to be retracted from a position over the surface of the substrate to the edge of the process bowl. The controller also causes the substrate to be rotated in a range of rates between about 50 revolutions per minute and about 1,000 revolutions per minute during the drying of the upper surface of the substrate. The controller also causes the substrate drying assembly to be retracted in a range of rates between about 1 mm per second and about 20 mm per second.
In another embodiment, an apparatus for drying a generally flat substrate that has been cleaned includes a rotatable support for supporting the substrate, a substrate drying assembly, and a controller. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is configured to position the liquid applying outlet and to position the vapor applying outlet above a portion of the substrate. The controller causes the substrate drying assembly to be retracted over the surface of the substrate at a range of rates up to and including a maximum rate. The maximum rate is increased as the rate at which the substrate is rotated is increased by about 0.5 mm per second for about each 100 increase in the revolutions per minute of the rotation of the substrate. The controller also is configured to cause the rotatable support to change the rate of rotation of the substrate while the substrate drying assembly is over the substrate.
In another embodiment, an apparatus for drying a generally flat substrate that has been cleaned includes a rotatable support for supporting the substrate, a substrate drying assembly, and a controller. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is configured to position the liquid applying outlet and to position the vapor applying outlet above a portion of the substrate. The controller applies at least one of a patterned substrate process window or a blanket substrate process window, causes the substrate drying assembly to be retracted over the surface of the substrate, and causes the rotatable support to change the rate of rotation of the substrate while the substrate drying assembly is over the substrate.
In another embodiment, an apparatus for drying a generally flat substrate that has been cleaned includes a rotatable support for supporting the substrate, a substrate drying assembly, and a controller. The substrate drying assembly includes a substrate drying assembly support arm, an outlet for applying liquid to an upper surface of the substrate, and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is configured to position the liquid applying outlet and to position the vapor applying outlet above a portion of the substrate. The controller causes the substrate to be rotated in a range of rates between about 50 revolutions per minute and about 1,000 revolutions per minute during the drying of the upper surface of the substrate. The controller causes the substrate drying assembly support arm in a range of retraction rates between about 1 mm per second and about 20 mm per second.
In another embodiment, an apparatus for drying a generally flat substrate that has been cleaned has a rotatable support for supporting the substrate, a substrate drying assembly, and a controller. The substrate drying assembly includes a substrate drying assembly support arm, an outlet for applying liquid to an upper surface of the substrate, and an outlet for applying a drying vapor to the upper surface of the substrate. The substrate drying assembly is configured to position the liquid applying outlet and to position the vapor applying outlet above a portion of the substrate. The controller causes the substrate drying assembly to be retracted over the upper surface of the substrate at a faster rate near a center of the substrate than near a periphery of the substrate.
In another embodiment, an apparatus for drying a generally flat substrate that has been cleaned includes a rotatable support for supporting the substrate, a substrate drying assembly, and a splashguard. The rotatable support is rotatable at a first rate and a second rate, the second rate being much greater than the first rate. The substrate drying assembly includes an outlet for applying liquid to an upper surface of the substrate and an outlet for applying a drying vapor to the upper surface of the substrate. The splashguard prevents splash-back onto the substrate when the rotatable support is rotating at the second rate.